Lightweight refractory castable is a castable mixture prepared from lightweight refractory aggregate and powder, binder and admixture. Due to its low bulk density, low thermal conductivity, and the convenience of construction of ordinary castables, With the advantages of less investment in production equipment, convenient disassembly and energy saving, it has been widely used as a thermal insulation material in many high-temperature projects. Compared with lightweight bricks, it has the advantages of small shrinkage, no brick joints or few brick joints, etc. In the high temperature industry, lightweight castables are more and more popular.

The most common are clay and light mullite castables, whose main properties are shown in the figure.

The factors affecting the performance of light mullite castables include the type, structure and properties of aggregates, the choice of binding system and the amount of addition, and the choice of additives such as water reducer. Among them, the lightweight aggregate plays a skeleton role in the lightweight castable, and the strength, bulk density and porosity distribution of the aggregate play an important role in the strength, thermal conductivity and post-burning line change of the lightweight castable. In addition, the common lightweight aggregates that are widely used at present contain a large number of open pores. During the molding process, part of the cement and water will enter the pores, which increases the consumption of cement and the amount of water added, and reduces the strength of the castable. It is difficult to obtain lightweight and high-strength lightweight castables using ordinary lightweight aggregates. Therefore, the development of lightweight aggregates with uniform pore distribution, small pore size, and closed pores is the key technology for preparing high-quality lightweight castables.
 
Application of high-strength lightweight mullite castables:

High-definition light mullite castables are mainly used in medium conversion furnaces and hydrogenation reactors in the chemical industry.
1. Hydrogenation reactor.
The hydrogenation reactor is an important equipment in the oil refining industry. The working temperature in the reactor is 500~600℃. It is equipped with catalytic medium, petroleum liquid and petroleum gas. It has a pressure of 8MPa and the working environment is very harsh. In the past, it mainly used light-weight castables configured with ceramsite and vermiculite, which often occurred spalling and network cracks, which caused the reactor surface temperature to exceed the limit and the furnace was shut down. After switching to cement-free high-temperature, high-strength light sedge castables, there was no problem from construction to baking.
There are cracks, and the furnace has been running for several months, and no cracks and spalling have been found in the shutdown inspection. continue to use,
2. Medium transformation furnace
In the chemical industry, the medium conversion furnace is a regenerative conversion device with a working temperature of 1200~1300 °C (sometimes to increase the output, the local temperature can reach more than 1300 °C), it is in direct contact with the flame, and there is a sprint of the gas flow inside. In the past, heavy high-aluminum castables were used for furnace linings, which had poor thermal insulation performance and large heat loss. After switching to lightweight mullite castables, after two years of use, users have responded well, and the heat storage and other effects are very good.